In a system for producing hydrogen or the like from a fuel by reforming the fuel to be fed into an engine, it is expected to enhance hydrogen producing efficiency because it makes an exhaust heat recovery system of reforming the fuel with an endothermic reaction of the fuel by making use of engine exhaust heat. Further, in a system of reforming a hydrocarbon fuel such as gasoline to produce hydrogen from the fuel and feeding a resultant gas as reformed gas including the hydrogen to an internal combustion engine, it is expected to heighten engine efficiency because it provides a way for the engine to make such as reduction of pumping loss, enhancement of combustion efficiency and enhancement of combustion speed. In a system where a reformer is installed in an exhaust pipe of an internal combustion engine, since exhaust gas temperature of the engine varies depending on engine operating conditions, the reforming efficiency varies depending on the conditions. For example, a conventional engine system with a reformer is disclosed in patent document 1. The engine system in patent document 1 is constituted in such a manner that the reformer is installed in the exhaust pipe at some distance from the engine and the reformed gas produced from the reformer is fed to an intake pipe together with exhaust gas.